| Shock ignition stands out from many ignition schemes,many works have been done on research on of shock ignition,the shock pulse,which is used to privede a strong shock wave in igniton is the key to fusion.For a typical shock pulse,the puls has a peak power of a 400 ~ 500 TW,pulse width ~ 200 ps,with energy of 100 k J.However,this 200 ps laser pulses' amplification put forward a big challenge.The traditional MOPA(Master Oscillator Power-Amplifier)amplification technology has low efficiency in energy extraction,while OP-CPA(optical parametric,chirped pulse amplification)technology is limited by its Fourier spectrum,both of the above are difficult to achieve efficient 200 ps laser pulses amplification.In order to solve this problem and meet the requirements of tshock ignition,a new technique to obtain high energy 200 ps lasers pulse based on stimulated Brillouin scattering(SBS)energy transfer is raised.This provides a practical research for the following "Shock Ignition" experimental set-up.This paper is mainly divided into the following parts:Firstly,Based on the SBS coupled wave equation,the energy transferring from the pump pulse to Stokes pulse in the Stimulated Brillouin Scattering process is deduced.Further,the numerical calculation model is constructed.Then,the influence of medium parameters,laser parameters and structural parameters on the energy conversion efficiency and power magnification in the SBS amplification process is numerically analyzed,which provides a theoretical reference for the design of the Brillouin amplification experimental system.Based on this theory analysis,the influence of the non-collinear angle on the Brillouin gain and the interaction length in the non-collinear SBS interaction is analyzed.The results show that high energy extraction efficiency can be got in large-angle Brillouin amplification by accurate frequency matching.Secondly,based on HIT 100 joule laser system,an active frequency matching SBS amplification is researched and verified.An optical fiber frequency-shift frontend that can generate 200 ps Stokes seed is developed.The frequency shifting frontend can meet the requirement of 100 picosecond pulse SBS amplification.This frequency shift device can be added to the front end optical fiber system to obtain the Stokes seed,the SBS energy transfer system is added before the terminal target,so that the energy is transferred to the ~200 ps Stokes pulse to construct the shock pulse for ignition.Thirdly,SBS amplification experiments based on active frequency-matching seed injection is researched.The experimental results show that : the stable 200 ps Stokes pulse seed can be obtained by optical fiber frequency shift.The SBS process can efficiently transfer the energy of the pumped pulse into the 200 ps laser pulses.Through a reasonable parameter design,The magnified power density can reach 6964 MW/cm2,with power amplification rate of 37.7 times,and energy amplification rate 18.4 times.While aiming at fusion,shock ignition experiment based on SBS amplification is designed.Finally,to solve the nonlinear competition in the Brillouin amplification process.theoretical analysis and experiments are carried out to investigate the nonlinear effects of small-scale self-focusing,SRS and nonlinear absorption in SBS amplification system,and the inhibition plan are proposed.The results show that the nonlinear refractive index,SRS gain coefficient and nonlinear absorption coefficient are also needed to considered while design SBS amplifier. |
PDF Full Text Request